Data Transmission – Practice Flashcards

A comprehensive set of 55 question-and-answer flashcards covering all major concepts from Chapter 2: Data Transmission, including packet structure, transmission methods, error detection, and encryption.

What is a datagram (data packet)?

A small unit of data used for transmission over a network, typically 64 KiB in size.

Why are data packets usually limited to roughly 64 KiB?

Smaller packets are easier to control and can be routed independently, allowing alternative paths if a route is busy or fails.

What is the main drawback of splitting data into packets?

The packets must be reassembled in the correct order at the destination.

Name the three main parts of a data packet.

Header, payload, and trailer.

List four items found in a packet header.

Sender’s IP address, receiver’s IP address, sequence number, packet size (and often total-packets indicator).

What does the payload of a packet contain?

The actual user data being transmitted (about 64 KiB per packet).

Give two functions of the packet trailer.

Marks the end of the packet and carries error-checking information.

Which error-checking method is commonly stored in the trailer of a packet?

Cyclic Redundancy Check (CRC).

Briefly describe how a CRC works.

Sender counts all 1-bits in the payload, stores the hex value in the trailer; receiver recalculates and compares—if values differ, the packet is resent.

Define packet switching.

A transmission method where a message is broken into packets that are routed independently through a series of routers to the destination.

How does a router choose a path for each packet?

It selects the shortest available route that is not congested or faulty, based on the destination IP address.

State two benefits of packet switching.

Lines are not tied up by one message, and packets can be rerouted around busy or failed links (also scalable and supports high data rates).

State two drawbacks of packet switching.

Packets can be lost or arrive out of order, causing reordering delays and problems with real-time streaming.

Define data transmission.

The process of sending data from a source to a destination via a communication medium (wired or wireless).

What are the three key factors considered in any transmission?

Direction of data flow, transmission method (bits at once), and synchronisation of data.

What is a protocol in networking?

A set of rules governing how data is transmitted so devices can communicate reliably and securely.

Name the three modes of data transmission direction.

Simplex, half-duplex, and full-duplex.

Describe simplex transmission.

Data flows in one direction only, e.g., computer to printer.

Describe half-duplex transmission.

Data flows both directions but not simultaneously, e.g., walkie-talkies.

Describe full-duplex transmission.

Data flows in both directions at the same time, e.g., broadband internet.

What is serial data transmission?

Sending one bit at a time down a single channel or wire.

Give one advantage and one disadvantage of serial transmission.

Advantage: Reliable over long distances with synchronised arrival. Disadvantage: Slower than parallel transmission.

What is parallel data transmission?

Sending several bits (often a byte) simultaneously across multiple channels/wires.

Why is parallel transmission unsuitable for long distances?

Different wires experience different delays, causing skew so bits arrive unsynchronised.

Name two contexts where parallel transmission is still used.

Inside computer circuits and short cable connections where high speed is essential.

What does USB stand for and what type of transmission does it use?

Universal Serial Bus; it uses serial data transmission.

Which two duplex modes are permitted by USB?

Half-duplex and full-duplex.

How many wires are in a standard USB cable and what are they for?

Four wires: two for power (red & black) and two for data (white & green).

List two advantages of USB-C over older USB connectors.

Reversible 24-pin design, supports up to 100 W power and 10 Gbps data (enabling 4K video).

Define an error in data transmission.

A situation where received data differs from the data that was sent.

Give three common causes of transmission errors.

Electrical interference, weak signals/noise, hardware faults or packet-switching problems (loss/skew).

Why must transmitted data be checked for errors?

Corrupted data can damage files, give wrong instructions, or cause data loss; computers need accurate data to function correctly.

Name the four main error-detection methods covered.

Parity checks, checksums, echo check, and automatic repeat requests (ARQ).

Explain an even parity check.

A parity bit is set so the total number of 1-bits (including the parity bit) is even; receiver recounts to detect odd-bit errors.

What limitation do parity checks have?

They detect only an odd number of bit errors; two flipped bits could go unnoticed.

Describe the checksum process in four steps.

Sender computes value with agreed algorithm, sends it with data; receiver recalculates checksum; if values match, data accepted; otherwise, data is resent.

Give one real-world use of checksums.

Verifying file integrity on downloads (e.g., MD5, SHA-256) or in TCP/IP packet headers.

How does an echo check work?

Receiver sends the received data back to sender; sender compares the echo with the original to detect discrepancies.

Why is echo checking considered unreliable?

If a difference exists, it is unclear whether the error occurred on the outbound or return path.

What is a check digit and where is it used?

A final digit calculated from the other digits in a code to detect entry errors; used in ISBNs, barcodes, credit-card numbers, etc.

List two common errors a check digit can detect.

Incorrect single digit entry and transposition of two digits (it can also detect missing or extra digits).

Briefly outline how the ISBN-13 check digit is generated.

Sum odd-position digits, sum even-position digits ×3, add both, find remainder ÷10; if remainder ≠0, subtract from 10 to get the check digit.

What does ARQ stand for and what does it do?

Automatic Repeat Request; it uses acknowledgements and time-outs to ensure corrupted data is retransmitted until received correctly.

Differentiate positive and negative acknowledgements in ARQ.

Positive ACK confirms correct receipt; negative ACK indicates error and requests retransmission.

Define encryption in the context of data transmission.

Transforming plaintext into ciphertext using a key so that only authorised users can read it.

Why is encryption essential for data sent over public networks?

It prevents intercepted data from being understood or modified by unauthorised parties (eavesdroppers).

Differentiate plaintext and ciphertext.

Plaintext is the original readable data; ciphertext is the scrambled, unreadable data after encryption.

What is symmetric encryption?

An encryption method where the same secret key is used to encrypt and decrypt data.

Give one advantage and one disadvantage of symmetric encryption.

Advantage: Fast, suitable for large data. Disadvantage: Key distribution problem—if the key is intercepted, security is broken.

What is asymmetric encryption?

Encryption that uses a public key for encryption and a private key for decryption, eliminating the need to share a secret key.

How does asymmetric encryption solve the key-distribution problem?

Only the public key is shared openly; the private key remains secret, so no confidential key needs to be transmitted.

Who can access the public and private keys in asymmetric encryption?

Everyone can access the public key, but only the key owner knows the private key.

Give one typical use for asymmetric encryption.

Secure web communications (SSL/TLS), digital signatures, or secure email.

Summarise the main difference between symmetric and asymmetric encryption.

Symmetric uses one shared key for both operations, while asymmetric uses separate public/private keys, enhancing key-exchange security.